Radioreceiver



June 289 1932. v sin. E. OSMUN ET AL.

RADIORECEIVER Filed Oct. 17, 1930 2 Sheets-Sheet 2 l N VEN TGR;

Patented .lune 28, i932 STATES PATENT OFFICE HORACE E. OSMUN, HARRY W. RUBIN STEIN, AND ERWIN R. STOEKLE, OF MILWAUKEE,

WISCONSIN, .ASSIGNORS TO CENTRAL RADIO LABORATORIES, OF MILWAUKEE, WIS- CONSIN, A CORPORATION OF WISCONSIN RADORECEIVER Application tiled October 17, 1930. Serial No. 489,272.

-This invention relates to improvements in radio receivers particularly to a device designed to improve the control of the overall ampliiication of the received signal.

lt is well lniown that the signal intensity at the antenna of a radio receiver varies Jfrom a few microvolts to several volts depending upon whether the receiver is located in the immediate vicinity ot the transmitting station or at a distance ot say one thousand or more miles. This makes the control of the volume of the amplified signal very diiiicult, since the total amplification of the signal has to be varied over a wide range. v

It has been the practice to control thesignal volume delivered by a receiver by attenuating the signal by means of suitable resistances at various stages oil the amplifier or at tpe antenna coil or to attenuate the signal at t e antenna by a separate local-distance switch which may change the tap to the` antenna coil or insert a condenser in series with the antenna. These expediente, however, have introduced complications in the structure of the receiver and in its control and have increased the cost of producin the receiver and for theseA reasons are un esirable.

@ne of the principal objects of the present invention is to provide a volume control for radio receivers having a single operating knob or element which, when turned to maX- imum volume position, will actuate a switch or its equivalent to increase the sensitivity of the receiver for distance reception and which when moved 'to the minimum volume position will reversely actuate the same switch to decrease the sensitivity of the receiver for local reception. And the same operating element or lmob is capable ot' eecting smooth and accurate regulation of the volume whether the receiverl is in a condition of maximum or minimum sensitivity,

, Broadly, the present invention resides in a radio receiver having means, usually but not necessarily, cooperable with the antenna for varying the volume of the signal impressed on the receiver, a local-distance switch regulating the action of said means and operable in one position to put the receiver in a condition et' maaimum sensitivity tor distant reception and in another position to put the receiver in a condition of minimum sensitivity for local reception, a manually operable volume control device usually in the form of a variable resistance and eiiecting smooth and -will automatically throw the local-distance switch into distance reception position and when the manually operable volume control device is moved to its minimum volume position it will automatically and reversely actuate the local-distance switch to decrease the sensitivity of the receiver for local rece tion. The invention is susceptible of cmbo iment in any of the various types of receivers and while in the present application three embodiments are illustrated it is to be understood that the particular types selected merely illustrate the invention and are not intended to restrict it to these particular types. For example, the manually operable volume control device utilized to effect a graduated regulation over the volume when the local-distance switch is in either position may consist of a potentiometer connected across the antenna receiving coil, a variable resistance connected with the grid circuits of the radio frequency amplifier to provide a variable negative potential 'for the grids with respect to their cathodes or a variable potentiometer resistance connected across the secondary of an audio transformer. The local-distance switch may carry out its function by connecting the antenna to its receiving coil directly s;

in one position or through a condenser connected in series between the antenna in its other position. Then again the local-distance switch may be utilized to change the coupling of the first tuned vacuum tube circuit to the antenna, that is, it may be applied to the so-called C-bias resistance utilized for volume'control purposes. lWhere the manually controlled volume device consists cfa variable potentiometer resistance connected f ilo across the secondary of an audio transformer its movable contact is operatively interconnected with the local-distance switch and the local-distance switch is connected up to the primary coil of the antenna whereby the manually controlled device automatically throws in all of the windings of the coil for distant reception and cuts out some of these windings and utilizes lonly a portion of the coil for local reception.

Other objects and advantages reside in certain novel features of the construction, arrangement and combination of parts which will be hereinafter more fully described and particularly pointed out in the appended claims, reference being had to the accompanying drawings, forming a part of this specification and in which:

Figure 1 is a diagrammatic view showing the invention embodied in a radio receiver having a volume control of the type wherein a potentiometer resistance is employed across the antennav receiving coil;

Figure 2 is a similar view showing the invention as applied to the so-called C-bias resistance for volume control purpose;

Fi ure 3 is a diagrammatic view showing the invention embodied in a radio receiver of the type in which volume control is effected by means of potentiometer resistance incorporated in the audio amplifier and by means of an arrangement of circuits for changing the coupling of the antenna coil with the first amplifier;

Figure 4 is a view partly in elevation and partly in transverse section showing one construction of manually operable volume con` trol device, local-distance switch and interconnecting means between the device and switch;

Figure 5 is a view in elevation looking toward the left hand side of Figure 4 with parts broken away for the sake of illustration;

Figure 6 is a view similar to Figure 5 but showing a different position of the parts;

Figure 7 is a view similar to Figures 5 and 6 bit showing the rear cover plate removed; an

Figures 8, 9 and 10 are detail perspective views showing the cover plate and local-distance switch, the movable arm of the manually operable volume control device and the rocking Contact thereof, respectively.

Referring to Figure 1, the potentiometer resistance 1 is shown connected across the antenna receiving coil 2 which furnishes the input voltage to the first vacuum tube 3 of a. radio receiver. The adjustable contact 4 on the potentiometer resistance can be moved from one end of the resistor to the other. A projection 5 on this movablecontact is arranged to engage the pawls `6 or 7 of the switch lever 8 when the arm is contacting at either end of the resistance 1. The lever 8 is pivoted at the point 19. When the Contact 4 is moved to the upper end of the resistance 1, the switch lever 8 is moved so that element 9 moves down intoelectrical contactwith 10. In this position the antenna conductor 12 is connected through 9,10 and conductor 13, directly to the upper end of the coil 2. Since the contact 4 is at the upper end of resistance l, this results in the grid of the vacuum tube 3 being connected directly to the antenna and receiving the full potential across the coil 2. This evidently is the condition for maximum sensitivity of the receiver and corresponds to maximum volume of signal output. With the switch contacts 9 and 10 connected we, therefore, have the so-called distance position of this switch. If the volume is too great, it can then be adjusted by moving contact 4 down, which, however, stillleaves the contacts 9 and 10 connected in the distance position.

If the operator happens to tune in a local station when the receiver is in the above condition of maximum sensitivity, a very loud signal will result. The operator will, therefore, move contact 4 down on resistance l, decreasing the volume until the maximum decrease obtainable with the volume control resistance is achieved, which is when contact 4 reaches the bottom of resistance 1. 'When this happens, however, the projection 5 engages the pawl 7 and throws the switch contacts 9 and 11 into connection. This throws the condenser 14 in series with the antenna and coil 2, thereby decreasing the potential across the coil 2 and also the sensitivity of the receiver. This connection of contacts 9 and 11 corresponds to the local position ofthe switch. If the operator now desires to increase the signal volume above the level obtainable under the above described conditions, he merely moves `contact 4 up on resistance 1, until the desired volume is obtained. In the above described manner the logical sequence of operations on the volume control of the receiver produces the required functioning of the local-distance switch automatically.

Figure 2 shows an arrangement of circuits wherein the same combination of volume control resistance and switching device changes `the sensitivity of the receiver by changing the coupling of the first tuned vacuum tube circuit to the antenna. In Figure 2 the rheo- Leeaevi may be allowed to pass through the resistance l5, although the diagram of Figure 2 illustrates the principle as applied to a two tube radio frequency amplifier. When the rheostat arm 4 is moved up to include maximum resistance projectionv 5 engages pawl 7 t0 cause contacts 9 and 11 of the switch to be connected together, and the receiver is in a condition of minimum sensitivity for local reception since the number of turns in the primary of the antenna coupling transformer is decreased. Conversely, when lthe contact 4 is moved down on the rheostat to increase the volume when seeking for distant stations, the projection 5 engages pawl 6 to cause the switch contacts 9 and 10 to be connected together at the end of the travel of 4. This corresponds to the distance position of the switch and after finding the desired station the volume can again be adjusted by moving 4 up until the desired signal volume is obtained.

It will be noted from the above description that the local-distance switch always remains in the position into which it is thrown at the ends of the travel of the rheostat arm, so that volume can be independently controlled in either the local or distance range of the receiver.

Referring to Figure 3, the primary 22 of an antenna coupling transformer is shown tapped by conductor 23. The conductor 23 leads to Contact 1l on the local-distance switch which is operatively related to the potentiometer resistance 25. Contact l0 of the switch is connected to the lower end of the antenna coil 22. Conductor 26 connects the switch arm to ground.

The potentiometer resistance is connected across the secondary of the audio transformer 27. The adjustable potentiometer contact 4 bearing onthe resistance 25 is connected to the grids of the last audio amplifier tube 28. In this manner the volume of sound output on the loud speaker may be increased or decreased as Contact 4 is moved to the left or right, respectively.

When the contact 4 is moved to its eX- treme left position, the projection 5 engages ,the pawl 6 and throws the switch contact 9 into connection with the contact 10 so that increased volume or maximum volume is had for when contacts 9 and 10 engage the entire antenna coil 22 is in series with the antenna and ground.. The volume may now be cut down by moving the Contact 4 to the right as lviewed in Figure' 3. If the receiver is tuned for local reception and intermediate adjustment of the contact 4 does not provide the desired reduction in volume the movement of contact 4 to its extreme right hand position as viewed in Figure 3 will bring itsprojection 5 into engagement with the pawl or dog 7 thereby swinging the movable switch contact 9 int engagement with contact 11, and consequently connecting the upper portion only of the primary coil 22 in series with the antenna and ground. This puts the receiver in condition for local reception or in a condition of minimum sensitivity and does this with the Contact 4 posi tioned so that adjustment of it to the left' will increase the volume if increase be desirable.

While Figure 3 shows only a single radio frequency stage, a detector and a single audio frequency stage, it is, of course, understood that any desired number of either radio frequency or audio frequency stages may be added to the circuit shown without chang ing the principle of operation of the device described.

Referring now to Figures 4 to 10, inclusive, there is shown one structure embodying a manually operable volume control device, a local-distance switch and an interconnecting means between these elements. The volurne control device is of the type disclosed in 'Patent 1,653,745, granted December 27, 1927, to Erwin R. Stoekle.

As illustrated, the volume control device includes a housing 30 referably constituted of bakelite or hard ruboer composition. The open rear end of the rear portion of the housing is closed by a cover plate 3l. A. graphite resistor 32 is mounted within the housing and corresponds to the resistor of potentiometer of Figure l, or to the resistance l5 of Figure 2 or to the resistance of potentiometer 25 of Figure 3. The ends of the graphite resistor 32 are electrically connected with terminals 33 and 34 to which the conductors are attached. The movable Contact is in the form of a rockable strip 35, the strip 35 being almost a complete circle and having inwardly extending arms 36 provided with an integral fork 37 and an integral attaching strip 38. Strip 38 is connected to a terminal 39 which is insulated, of course, from the terminals 33 and 34. The fork 37 en gages between insulating Washers 39 carried by a flange ring 4() which is mounted on the operating shaft 41. As will be seen from. Figure 4, the attaching strip 38 is fastened by the rivet 38" which connects it to its terminal 39 on a boss or lug 39 and consequently the disc-like movable contact 35 is biased to a position spaced from the resistor 32 and any portion of this strip 35 is engaged with the resistor under the influence of a rotatable switch arm 42 fixed to the inner end of a shaft 41 and having a button 43 adapted to slide around the strip 35 and press any portion of this strip against the portion of the resistor 32 underlying the same. For limiting the motion of the switch arm 42 and preventing its button 43 from running off of the strip 35, the hub of the arm 42 is slotted as at 45 and a fixed stop lug 46 carried by the base projects into this lll) slot. The lug 46 engages the ends of the slot to positively limit movements of the switch arm.

The contacts of the local-distance switch, designated at 10 and 11, are mounted on the inside of the cover plate 3l and connect with terminals or binding posts 47 and 48 mounted on the outside of the cover plate. The movable contact of the local-distance switch is designated at 9 and is pivotally connected as indicated at 50 to the cover plate. The movable contact 50 is in electrical connection with the cover plate but the contacts l0 and 11 and their terminals 47 and 48 are electrically insulated from the cover plate. The binding post of the movable contact 9 is designated at 5l and is directly connected to the cover plate 31. The automatic operation of the local-distance switch from the manually operable controlled device may be effected by providing a projection 55 on the movable switch arm and disposing this projection to engage av pawl or lug 56 when the switch arm is at the limit of its movement in one direction and to engage a pawl or lug 57 when the switch arm is at the limit of its movement in the opposite direction. It is to be understood that the projection 55 engages either lug 56 or 57 when it is just approaching the end ot its motion in one direction and when the switch arm still may be moved suficiently to shift the movable contact 9 from contact 10 to contact 11 or from contact 1l to contact 10, as the case may be.

It is to be understood that the structure shown in Figures 4 to l0 is merely illustrative of one embodiment of the invention and that various changes in the sizes, shape, form and arrangement of the parts may be made without departing from the spirit of the invention or the scope of the subjoined claims.

It is obvious that the contacts 10 and ll and the terminal 5l of the local-distance switch may be connected up in the receiver as illustrated in Figures l, 2 or 3, or in any other appropriate manner. Likewise the ter-y minals 38, 34 and 39 of the variable resistance or potentiometer are connected up in the receiver in the manner illustrated in Figures 1,2 or 3, or in any other appropriate manner.

The invention claimed is: l. A radio receiver having means cooperable with the antenna for varying the volume of the signal impressed on the receiver, a'

manually operable volume control device and the local-distance switch whereby when the manually operable device is moved to its maximum volume position it will automatically throw the local-distance switch into distance reception position and when the manually operable control device is moved t0 its minimum volume position it will automatically and reversely actuate the local-distance switch to decrease the sensitivity of the receiver for local reception.

2; A radio receiver having means including a local-distance switch and operable with the local-distance switch in one position to put the receiver in a condition for maximum sensitivity for distance reception, and in another position to put the receiver in a condition of minimum sensitivity for local reception, a manually operable control device associated with the receiver for etfecting graduated and accurate regulation of the volume when the receiver is in a condition of maximum or minimum sensitivity and means interconnecting the manually operable control device and the local-distance switch when the manually operable control device approaches either of its extreme positions whereby the manually operable control device automatically operates the local-distance switch when moved to either extreme position.

i 3. A radio receiver having a local-distance switch, a manually operable volume control` and means actuated by the manually operable volume control for automatically moving 'the local-distance switch to one position when the manually operable volume control approaches one predetermined position and for throwing the local-distance switch to another position when the manually operable volume control is moved to a second predetermined position.

4. A radio receiver provided with manually controlled means for attenuating the strength of the amplified received signal, said attenuating means including a switching means and means automatically operated by said manually controlled attenuating means to put said receiver in a condition of maximum sensitivity' for distant reception or in a condition of lesser sensitivity for local reception.

5. A radio receiver having a volume control device, a local-distance switch, and means operatively relating said volume control device'and said local-distance switch whereby said switch will be automatically thrown into the distance reception position wheii said volume control is moved to its position of maximum volume and will remain in this position until said volume control is moved into its position of minimum volume whereupon said switch will be thrown into its local reception position and will so remain until said volumey control is again moved to its maximum volume position.

6. A radio receiver including a variable resistance for attenuating the signal, means Leeaa'n 5 for varying said resistance, means cooperable from the manually operable volume control.

with an antenna receiving coil for varying the volume ot the signal impressed on the receiver and a switch controlling the action of said means and automatically operated by said first named means.

7 A radio receiver provided with a volume control device operatively related to a localdistance switch and adapted to throw said switch into its distance and its local position at the maximum and minimum positions, respectively, of said volume control whereby the volume of the ampliiied receiver signal may be regulated independently over the entire local range of sensitivity ot the receiver and over th-e entire distance range of sensitivity ot the receiver.

8. A radio receiver including an antenna, an antenna receiving' coil, a vacuum tube` a potentiometer resistance connected across the antenna receiving coil and having a movable contact connected to the vacuum tube to supply the input voltage thereto. a 'condenser and a switch for connecting' the antenna to its receiving coil through the condenser and for connecting the antenna directly to its receivina coil and cooperating means between the movable contact of the potentiometer and the switch for causing the switch to be automatically operated when the movable contact approaches either ot its extreme positions.

9. A radio receiver including a radio trequency amplifier vacuum tube` a so-called variable C-bias resistance for varying the nega# tive potential ot the ,arid ot said tube with respect to its cathode. an antenna coupling transtormer. electrical connections for eonnecting the entire primary ot said transiiormer or a portion only thereot tothe ground and a switch for making and breaking said circuits and connected with the variable resistance so as to be operated when said variable-resistance is in either of its eXtreme positions. v

l0. radio receiver' including an antenna coupling transformer. an audio transt'ormer` a variable potentiometer resistance connected across the secondary ot the audio transt'ormer` electrical connections for connecting` the entire primary ot the an'tenna coupling transformer or a portion only thereo't to the ground and a switch controlling said electrical connections and automatically operated by the potentiometer.

1l. A radio receiverhavinpjalocal-distance switch including a movable contact provided with spaced projections, and a manually operalole volume control having a movable element provided with a projection engageable with one of the projections of the Contact switch in one position ot the manually operable volume control and engageable with the other projection of the switch in another position of the volume control. whereby the local-distanee switch is automatically operated In witness whereof, we hereto aiiix our sig- HORACE E. OSMUN. HARRY W. RUBINSTEIN. 70 ERWIN lt. STGEKLE.

natures. 

